1. Field of the Invention
The invention relates to a light-emitting device in which a phosphor and a light-emitting element are used and a method of manufacturing the same, and in more particular, to a light-emitting device in which a phosphor and a light-emitting element are used to produce white light and a method of manufacturing the same.
2. Related Art
In so-called COB (Chip-on-Board) modules, plural light-emitting elements such as LED chips are mounted on a general-purpose substrate such as ceramic substrate or metal substrate. In LED lamps, a light-emitting element is mounted on a resin or ceramic package. In light-emitting devices such as COB modules or LED lamps, an LED chip emitting ultraviolet to blue light is used and a phosphor is contained in a sealing portion sealing the LED chip. Phosphor particles are excited by light emitted at the time of driving the light-emitting element and emit a desired wavelength-converted light in blue to red color, and white light is obtained as a mixed light of the light of the light-emitting element and the wavelength-converted light or as a mixed light of the wavelength-converted lights only. As such, in recent years, use of phosphor has become the mainstream when white light is obtained using a light-emitting element.
The following three typical methods are known as a measure to incorporate phosphor particles into a sealing portion. Here, examples of applying these methods to an LED lamp will be described.
In the first method, an LED chip 2 is mounted on a package 1 and phosphor particles 3a are arranged in a sealing portion 3 on a LED chip-mounting side, as shown in FIG. 1A (hereinafter, referred to as a “precipitation arrangement”). The precipitation arrangement has an advantage in that it is possible to convert a wavelength of the phosphor particle 3a at high efficiency since the phosphor particles 3a are arranged in the vicinity of the LED chip 2 (see, e.g., JP-A-11-040858, JP-A-2007-227791, JP-A-2009-016779 and JP-A-2012-114416).
In the second method, the phosphor particles 3a are arranged so as to be uniformly dispersed in the sealing portion 3, as shown in FIG. 1B (hereinafter, referred to as a “dispersed arrangement”). This method has an advantage in that it is easy to control color of the light-emitting device (see, e.g., JP-T-2005-524737).
In the third method, the phosphor particles 3a are arranged in the sealing portion 3 at a position away from the LED chip 2 which is mounted on the package 1, as shown in FIG. 1C (hereinafter, referred to as a “separate arrangement”). The separate arrangement has an advantage in that color unevenness due to change in visual angle when viewing the LED lamp from an observer side can be prevented (see, e.g., JP-T-H11-500584).
When the LED lamp is emitting light, heat is built-up in the LED lamp due to heat generated by driving the LED chip 2 and heat generated by wavelength conversion of the phosphor particles 3a. This causes problems in that the sealing portion 3 or other components, such as LED chip 2, constituting the LED lamp deteriorate, resulting in a decrease in brightness and reliability of the LED lamp. Therefore, as a measure against heat generation in the LED lamp, heat is generally dissipated from a mounting surface of the LED lamp through a lead 1a which is a portion for mounting the LED chip 2. This method is also used for the COB module in the same manner and heat is generally dissipated from a wiring on a ceramic substrate or a mounting surface of a metal substrate which constitute the LED lamp.